Crystallization holds the potential to be used for protein purification and low-viscosity drug substance and drug product formulations. Twenty-two different proteins (20 monoclonal antibodies and two Fc-fusions) were examined to determine the breadth of applicability of crystallization to these therapeutic proteins. Vapor diffusion technique and an evaporative screening method were used to identify crystallization conditions using around a 100 initial conditions based on reagents that are generally regarded as safe (GRAS). Of 16 IgG(2)s examined, at least four formed diffraction-quality crystals and four others formed crystal-like particles. At least three of the IgG2s that crystallized well were also crystallized under the same set of operating conditions using inexpensive GRAS reagents. The crystals were formed to high-yields in a few hours and were dissolved quickly without impacting product quality. Although only a fraction of the proteins examined crystallized, all exhibited liquid-liquid phase separation (LLPS), which could be used for their concentration or possibly purification. One of the Fc-fusions, for example, was concentrated by LLPS to a self-buffering solution at 150 g/L. Crystallization and LLPS in the salting-in region were shown to be feasible. (C) 2011 American Institute of Chemical Engineers Biotechnol. Prog., 27: 1054-1067, 2011